1. Field of the Invention
The present invention relates to a spindle motor, and more particularly, to a spindle motor in use for optical disk drive which can reduce the vibration induced from eccentricity.
2. Description of the Related Art
In general, a spindle motor in use for an optical disk drive serves to turn an optical disk so that an optical pickup can read data from the optical disk while moving linearly.
When the spindle motor turns the optical disk at high speed, any unbalance of the optical disk may generate vibration, and thus the Ball Auto Balance System (Ball ABS) is adopted to reduce such vibration.
According to the principle of the ball ABS, a predetermined number of balls are received in an integral turntable for turning an optical disk mounted thereon, by which when the optical disk is rotated, the balls are driven in a direction counter to the eccentricity of the optical disk in order to reduce any vibration induced from the eccentricity of the optical disk.
FIG. 1 is a sectional view illustrating conventional spindle motor structure, and FIG. 2 is an enlargement of a part A in FIG. 2.
Referring to FIGS. 1 and 2, in the conventional spindle motor in use for an optical disk drive, a stator includes a base plate 10 for fixing the spindle motor, a bearing housing 20 arranged in the center of the base plate 10 and having a metal bearing 21 installed therein and a core assembly 23 mounted on the outside wall of the bearing housing 20.
The core assembly 23 includes a plurality of cores and winding coils 23a. 
On the top of the base plate 10, there is installed a Printed Circuit Board (PCB) 11 for applying control voltage to the winding coils 23a. 
By the flow of a predetermined value of current via the PCB 11, the winding coils 23a generate magnetic flux.
A shaft 40 is rotatably coupled with the metal bearing 21 mounted within the bearing housing 20, and a rotor yoke 31 is fixed to the shaft 40 extended beyond the bearing housing 20 to rotate along with the shaft 40.
The rotor yoke 31 is cylindrical shaped to surround the tops and sides of the bearing housing 20 and the core assembly 23, and has a magnet 33 attached on the inside surface opposed to the core assembly 23 to constitute a rotor 30.
The magnet 33 has a plurality of N and S poles repeatedly alternating with each other to generate magnetic flux, which in turn interacts with the magnetic flux from the core assembly 23 thereby to rotate the rotor 30.
A turntable 50 is fixed around the shaft 40 extended above the rotor yoke 31 to rotate along with the rotor 30.
The turntable 50 has a buffer member 51 attached on the top thereof to buffer the impact at the mounting of the optical disk and prevent the slippage of the optical disk during the rotation. The turntable 50 also has a ball container 53 on the bottom periphery thereof to receive a suitable number of balls B and a ball cover 54 coupled with the bottom of the ball container 53 to prevent the balls B from escaping from the ball container 53.
The ball container 53 is shaped as a circular track so that the suitable number of balls B inserted into the ball container 53 move and rotate along the circular track in response to the rotation of the turntable 50.
The turntable 50 further has a clamp 55 that is fastened with the top of the shaft 40 to prevent the turntable 50 from escaping from the shaft 40.
The operation of the conventional disk drive motor of the above construction will be described as follows.
First, a voltage applied to the spindle motor is fed to the winding coils 23a of the core assembly 23 via the PCB 11.
By the flow of current, the winding coils 23a generate magnetic flux, which in turn creates magnetic force through interaction with the magnetic flux from the magnet 33 placed in the inside surface of the rotor yoke 31 opposed to the core assembly 23 thereby to rotate the rotor 30.
That is, the rotor 30 is rotated under the electromagnetic force originated from the interaction or link between the magnetic fluxes from the winding coils 23a and the magnet 33.
The rotation of the rotor 30 also cause the shaft 40 coupled with the rotor 30 to rotate, and thus the turntable 50 fixed to the shaft 40 rotates.
This in turn rotates the optical disk recorded with various data, seated on the buffer member 51 of the turntable 50.
In this case, since any unbalance of the optical disk may create vibration, a Ball Auto Balance System (Ball ABS) is adopted to prevent the vibration.
That is, if vibration occurs from the eccentricity of the optical disk, the balls B inserted into the ball container 53 in the bottom periphery of the turn table 50 move in a direction counter to the eccentricity of the optical disk to calibrate the eccentricity thereby reducing vibration.
The ball container 53 receives about 10 balls B. During the rotation of the turntable 50, the balls B move along an outer wall 53a of the ball container 53 in a direction counter to the eccentricity of the optical disk to automatically balance the optical disk.
However, the conventional optical disk drive as described above has a following problem. At the time of opening a tray for the purpose of removing or replacing an optical disk, even after the turntable has stopped its rotation, the balls B contained in the ball container 53 continuously roll under the inertia creating noises.